java - Calculate age in Years, Months, Days, Hours, Minutes, and Seconds

Question

I need to take a birthday entered by the user (preferably in dd/mm//yyyy format) and find their age, based on todays date. Could someone explain to me the process I should go through to find this? I need to print it out in the format:

"You are 19 years, 4 months, 12 days, 8 hours, 44 minutes, and 39 seconds old."

I'm just a little confused on how I would subtract a date from another date, and how I would reference each part (years, months, days, hours, etc) separately.

The code I have at the moment for reference:

import java.sql.Date;
import java.text.DateFormat;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.Calendar;
import java.util.Scanner;

public class Driver {

    public Driver(){}

    public static void main( String[] args){
    Driver menu = new Driver();
    MenuOptions option;
    do{
        menu.displayMenu();
        option = menu.getResponse();
        menu.runOption(option);
    }while(option != MenuOptions.Quit);  
    }

    private enum MenuOptions{
    AgeCalc("Calculate your age"),
        AnniversaryCalc("Calculate time until specified date"),
        AgeDifference("Find the time between two specified dates"),
        Quit("Exit the program");

    private String value;

    private MenuOptions(String value){
        this.value = value;
    }

    public String toString(){
        return value;
    }
    }

    public void displayMenu(){
    for(MenuOptions option : MenuOptions.values()){
        System.out.printf("%5d: %s
", option.ordinal()+1, option);
    }
    }

    public MenuOptions getResponse(){
    int value = -1;
    Scanner input = new Scanner(System.in);

    do{
        System.out.println("> ");
        String response = input.nextLine();

        if(response.matches("\d+")){
        value = Integer.parseInt(response);
        if(value < 1 || value > MenuOptions.values().length){
            value = -1;
            System.out.println("Unknown response, please enter a number between 1 and " +MenuOptions .values().length);
        }
        }

    }while(value <=0);

    return MenuOptions.values()[value-1];
    }

    public void runOption(MenuOptions option){
    Scanner in = new Scanner(System.in);

    switch(option){
    case AgeCalc:
        System.out.println("Please enter your birthday mm/DD/yyyy).");
        System.out.println(">");

        DateFormat df = new SimpleDateFormat("mm/DD/yyyy");

        try
        {
            java.util.Date birthday = df.parse(in.nextLine());           
            System.out.println("Today = " + df.format(birthday));
        } catch (ParseException e)
        {
            e.printStackTrace();
        }
        Calendar today = Calendar.getInstance();
        java.util.Date today = df.format();

        DateFormat simple = new SimpleDateFormat("dd/MM/yyyy");
        String birthdate = simple.format(in.nextLine());
        Date.parse(birthdate);

        System.out.println(birthdate.toString());
        break;
    case AnniversaryCalc:
        System.out.printf("PI: %.20f
", Math.PI);
        break;
    case AgeDifference:
        for(int p=0; p <= 32; p++){
        System.out.println("2^" +p+" = " +Math.pow(2,p));
        }
    }
    }
}

Answer 1

I'd suggest using Joda time. It's a much better API than what's included in the JDK.

Create an Instant representing when the person was born, another representing the current time, and use those two Instants to create a Period. From there it's easy to get the fields you need using the methods provided in the Period class.